1Department of Neuroscience and Physiology, Institute of Psychiatry and Neurochemistry, The Sahlgrenska Academy, University of Gothenburg, 40530 Gothenburg, Sweden2Department of Philosophy, Linguistics and Theory of Science, University of Gothenburg, 40530 Gothenburg, Sweden

Received 18 September 2012; Revised 13 November 2012; Accepted 13 November 2012